I was struggling to be the tech-support for my mother back home and getting her to talk to me over magic jack. It kept saying, Error 9: no internet connection.
And yet at the same time she could hear me properly on Skype but I was not able to hear her at all. Video was working both ways.
I asked her to unplug the magic jack ("Safely remove hardware" and all), and viola, the skype audio started working! :)
I haven't ascertained yet, but I am pretty sure the solution to the magic jack also lies somewhere there - some other device must be using the network itself.